conversions are different but UST and other tubeless rims are meant to retain the tyre (in the event of deflation) by virtue of the lip in the shoulder of the rim. If this works OK it seems to me that it doesn't really matter if the well is deep or not.
BTW it appears to be not well understood (in cycling circles at least) that the security of the tyre on the rim, and that the hooked bead had any tyre-retaining effect whatsoever, is entirely contingent upon where a tubeless tyre actually seals.
If the tyre has a lip at the bead edge that seals in the well of the rim, tyre pressure is pushing the bead into the hooked part of the rim, and the tyre is well retained.
If however the pressure seal is at the edge of the rim (and IME it can be with all kinds of tubeless tyres that are mounted on rims with imperfect wells) then there is no air pressure force pushing the tyre bead into the rim hook; the pressure is the same on both sides of the tyre bead. Even with the thinnest tape, it seems likely that the tyre won't seal perfectly against the rim well where the tape finishes.
If the bead lifts out of the rim well at all, once the tyre is fully inflated, the well seal will be lost and the tyre won't be well retained.
I suppose that this might explain why some tubeless bicycle setups are just not reliable; there have been quite a few reports of widish tyres at highish pressures just blowing off the rim without warning.
To combat this kind of thing even tighter fits of tyres (with remotely stretchy beads) on rims are required, and/or tyre beads that are much less stretchy. There are moves afoot in this direction; dedicated tubeless bicycle tyres in many cases are getting heavier, with more rubber in the sidewalls, and more material to make a less stretchy tyre bead.
Anyway none of this requires that the rim well be shallow, does it? It does not appear to play a large role in sealing, or in (useful) tyre retention once deflated; it arguably just makes the tyre difficult to get on and off the rim.
cheers